Haoran Yu

Switchable and tunable film bulk acoustic resonator fabricated using barium strontium titanate active layer and Ta2O5/SiO2 acoustic reflector

A solidly mounted acoustic resonator was fabricated using a Ba0.60Sr0.40TiO3 (BST) film deposited by metal organic chemical vapor deposition. The device was acoustically isolated from the substrate using a Bragg reflector consisting of three pairs of Ta2O5/SiO2 layers deposited by chemical solution deposition. Transmission electron microscopy verified that the Bragg reflector was not affected by the high temperatures and oxidizing conditions necessary to process high quality BST films. Electrical characterization of the resonator demonstrated a quality factor (Q) of 320 and an electromechanical coupling coefficient (Kt2) of 7.0% at 11 V.

Evaluation of Phase Segregation in Ternary Pt-Rh-SnO2 Catalysts Prepared from the Vapor Phase

Ethanol holds promise as a non-toxic, transportable, energy dense (8kWh/kg) fuel that, unlike hydrogen, is amenable to use in the existing fuel infrastructure. However, slow oxidation kinetics and incomplete CO2 formation, indicating unbroken C-C bonds at practical potentials, limit usage in a fuel cell. Incomplete formation of CO2, a complete 12 electron transfer, leads to the formation of adsorbed intermediates such as CO, acetaldehyde, and acetic acid. These intermediates can poison the catalyst surface leading to a loss in cell efficiency. The use of Pt/Rh/Sn ternary catalysts has proven promising owing to bi-functional, electronic, and synergistic effects between the constituents. The role of Rh is to cleave the C-C bond of ethanol, SnO2 provides the OH species to oxidize intermediates (freeing the Pt and Rd sites), and Pt is for ethanol dehydrogenative adsorption [1].

Transmission Electron Microscopy Study on Platinum Nanoparticle Distribution in PEMFC Catalyst Layers under Different Ionomer/Carbon Ratios Fabricated by Direct Dry Deposition

Proton exchange membrane fuel cells (PEMFC) are poised for market penetration in the automobile, portable and back-up power markets. Cost and durability issues are crucial to the performance of PEMFC, which primarily depends on the design of catalyst layers [1]. Current catalysts layers use platinum (Pt) supported on high-surface-area carbons (e.g., Ketjen Black® and Vulcan®) with perfluorosulfonic acid (PFSA) ionomer as a binding agent. It is widely believed that incorporation of ionomer can extend the reaction zone, increasing the proton conductivity and catalyst utilization [2]. The catalyst layers are predominately comprised of primary carbon particles, 20-50 nm in diameter. Stacking of primary carbon aggregates creates a unique 3D structure between the fractal structured carbon branches [3]. Depositing the carbon with Pt nanoparticles can block these micropores since the size of the Pt particles ranges between 2-4 nm. The PFSA ionomer is distributed on the surface of carbon agglomerates and covers intra-agglomerate pores (<20nm) at lower ionomer content, e.g., below 30 wt.% ionomer. Significant blocking of the pores is observed with higher ionomer content (>50% wt.) [4].